The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the inventors hereof, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted to be prior art against the present disclosure.
Physical transceivers that operate on a single twisted wire pair cable is a new application of LANs in the IEEE 802.3 (Ethernet) standard. The single pair cable conveys signals from one transceiver to another via a dual duplex channel. The IEEE 802.3 (Ethernet) Working Group has two active task forces in this area addressing 1 Gigabit and 100 Megabits over a single twisted pair cable, i.e., 1000BASE-T1 and 100BASE-T1. As a transceiver can operate at multiple rates, two devices connected by a cable can negotiate a commonly supported rate for both devices to operate on.
Transceiver performance in a single twisted pair application can be impaired by multiple sources of degradation. First the single twisted pair may be used to convey a voltage across the differential pairs along the length of the cable, e.g., the power over differential line (PoDL). The PoDL system requires a scheme to block the direct current (DC) voltage source from the transceiver. PoDL can also introduce significant noise at low frequencies into the transmission system that can degrade transceiver performance. A high pass network or isolation device such as capacitors or a magnetic transformer can be used to isolate the transceiver from the DC voltage supplied to the differential wire pair. The isolation device may attenuate low frequency signals between the transceiver and the differential wire pair. An example can be a first order high pass filter (HPF) at the cutoff frequency of 10 MHz. In a system using PoDL with the 10 MHz HPF, the communication channel is no longer suitable to implement typical baseband line codes such as Non-Return to Zero (NRZ) or IEEE 802.3 Clause 73 differential Manchester encoding (DME) with a conventional receiver architecture, because significant low frequency energy can be lost. Data recovery can thus be difficult and system bit error performance is degraded.
Second, the system can be impaired by multiple broadband noise sources such as thermal noise, which is typically modelled as additive white Gaussian noise (AWGN).
Third, the system can be impaired by radio frequency narrow band interferers (NBI), which can couple onto the twisted pair and appear as an undesired signal at the receiver in addition to the desired signal and AWGN. The NBI is typically modeled as a sine wave. The levels of NBI in the single twisted pair transceiver application can be significant, relative to the transmit signal of the transceiver. For example, a NBI signal of 200 mV can occur to a 1V nominal transmit level.
Fourth, the twisted pair cable itself may attenuate higher frequencies and distort the transmitted signal introducing inter-symbol interference (ISI) at the receiving transceiver.